3.2.1

Force update-cache refresh before upgrading a plugin

handle_update_plugin_request() called Plugin_Upgrader::upgrade()
without refreshing get_site_transient('update_plugins') first. With a
stale/empty cache, the upgrader finds no known update for the plugin
and returns null, which the handler reports as "Déjà à jour" even
though the real latest version was never downloaded — observed with
Headspin Copilot reporting success remotely while staying on the old
version on the actual site. Mirrors the same fix already applied to
handle_status_request(). Bump to 3.2.1.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>